A very thin layer of "Honda Shin-Etsu Grease" works great for lubricating and eliminating seal creaks during body flex. Wipe a tiny amount on the seal, rub it in, and wipe off excess with a clean rag. You'll think there's so little grease remaining that it couldn't possibly make any difference, but it definitely does. Shin-Etsu grease is routinely recommended on car forums if you want to read up on it.